This application relates generally to disc drives. More particularly, this application relates to the optimization of writing or transmitting data.
Disc drives have magnetic media on discs that are rotated while read and write heads communicate magnetic signals to and from the magnetic media on the surfaces of the rotating disc. The magnetic signals are generally written in tracks arranged in generally concentric circles about the center of rotation of the magnetic disc. During manufacturing, servo bursts are written onto the magnetic disc to divide the disc into several arcuately spaced radial wedges. A set of data sectors is then written onto each track in the wedges between the servo burst wedges. Each servo burst contains information that identifies the track that the head is positioned over as well as position data that indicates the position of the head relative to adjacent tracks and the centerline of the current track.
A servo control system typically controls the rotational position of a rotary actuator to position the head over the desired track and maintains that position during the read or write process for data from or to the desired track. The servo control system utilizes the servo burst information to maintain the head""s position directly over the desired track by detecting whether the head is straying from the track centerline and by applying a correction to the actuator to correct the head""s position.
During track-following which occurs during read or write processes, the head reads position related information at each servo burst which may be converted by a state estimator, with reference to currently and previously measured and predicted values, into a predicted current position, velocity, and acceleration for the head and possibly other parameters as well. From these position related values, it can be determined whether the head position had an unacceptable chance of exceeding the bounds of the track in the previous wedge or whether the head position has an unacceptable chance of exceeding the bounds of the track in the subsequent or following wedge. The head may move beyond the side to side bounds of the track for many reasons such as shock events that impose an unexpected force upon the actuator. Furthermore, the head position may appear to have exceeded the bounds of the track because a servo burst is bad even though the head may have remained on-track.
During a data writing operation, a conventional disc drive control system first determines whether the head has the appropriate position values such that the data written in the data sectors of the previous wedge was properly on-track. The control system also determines whether the head is in the appropriate position and dynamic state such that the data to be written in the following wedge will be properly on-track. If the first determination indicated that the head exceeded the track bounds of the previous wedge or that the head will exceed the bounds in the following wedge, the data in the previous wedge is not validated and the write is retried. The data for both the previous wedge and the following wedge remains in the disc drive buffer and after a revolution of the disc, the disc drive control attempts to rewrite the data and then again determines whether the head remained in-bounds for the previous wedge and whether it will continue to remain in-bounds for the following wedge.
Typically, this retry for the previously written data and the data for the following wedge is not troublesome because the disc drive can maintain the data to be rewritten in the buffer and can indicate to the host that data should be withheld from the disc drive until the buffer has vacancies. However, when the data is time-critical, such as in cases where the data streams to the disc drive and cannot be temporarily stopped at the source (i.e., digital cable), the extra time that the previously written data remains in the buffer would result in a loss of data that is streaming to the disc drive if the buffer has no vacancies. In most time-critical situations, the data to be received and written to the disc will far exceed the capacity of the buffer. Thus, the extra revolutions required for rewrites during which the data to be rewritten remains in the buffer results in incoming streaming data having no place to go and therefore, being lost.
Accordingly there is a need for a method that improves the disc drive""s ability to handle writing of time-critical data.
Against this backdrop, embodiments of the present invention have been developed. The disc drive embodiments of the present invention involve independently deciding whether to qualify the data in just-written sectors in one wedge between servo bursts and deciding whether to allow writing of sectors in the next wedge between servo bursts. Alternatively, the data handling embodiments of the present invention involve independently deciding whether to qualify data just transmitted and whether to allow transmission of the next data.
An exemplary method for writing data in accordance with the present invention to a disc in a disc drive that has a transducer head, a buffer containing the data, and a plurality of tracks and servo bursts defined on the disc involves several steps. The method involves first writing data to a plurality of data sectors between a first servo burst and a second servo burst on a track. The recoverability of data written between the first and second servo bursts is then determined. Buffer locations containing data written in one or more of the plurality of data sectors between the first servo burst and the second servo burst is released from the buffer are made available if the recoverability is acceptable. Then an amount of encroachment of the head upon an adjacent track between the second servo burst and a third servo burst is predicted, and data is written to one or more data sectors between the second servo burst and the third servo burst only if the amount of encroachment is within predetermined acceptable units.
An exemplary disc drive for writing data to a disc in accordance with the present invention has a plurality of tracks and servo bursts and a buffer configured to hold the data to be written to the disc. The disc drive also includes a transducer head having a controllable position and configured to write a plurality of data sectors between a first servo burst and a second servo burst on a track. A processor is also included and is configured to determine a recoverability of data written between the first and second servo bursts and to make buffer locations holding the data written in one or more data sectors between the first servo burst and the second servo burst available if the recoverability is acceptable. The processor is further configured to predict an amount of encroachment of the head upon an adjacent track between the second servo burst and a third servo burst and to cause the head to write data to one or more sectors between the second servo burst and the third servo burst if the amount of encroachment is within predetermined acceptable units.
An exemplary data handling system for transmitting data from a first location to a second location in accordance with the present invention has a transmission medium linking the first location to the second location that is configured to carry the data being transmitted. A statistical dependence in a transmission quality exists between temporally-close periods of transmission through the medium. The data handling system also includes a processor configured to detect information about a prior transmission period, generate a first probability estimate that data was successfully transmitted in the prior transmission period, and determine whether to cause a retransmission of data transmitted in the prior transmission period based on the first probability estimate. The processor is further configured to predict a capability of a next transmission period, generate a second probability estimate that data will be transmitted successfully in the next transmission period, and determine whether to attempt transmission during the next transmission period based on the second probability estimate.
These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.